Import CSTLogicError and BaseMetadataProvider from their defining modules

[haampie-bot]

Summary

import libcst only works because of the import order in libcst/__init__.py. Moving from libcst._nodes.base import ... above from libcst._exceptions import ... gives:

ImportError: cannot import name 'CSTLogicError' from 'libcst'

Modules in _nodes and _parser import CSTLogicError from libcst, and metadata/reentrant_codegen.py imports BaseMetadataProvider from libcst.metadata. This PR imports both from their defining modules.

Test Plan

• Moved each import in each __init__.py to the top and imported the package. 9 of these moves fail on main, none on this branch. Found with uncycle.
• The tests give the same results before and after. ufmt check and flake8 pass.

AI disclosure: made with Claude (Anthropic). Opened from a bot account on behalf of @haampie.

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